Determining Ratio

[tkpinsc]

So when cruising, I've been riding by the tach and not so much the speedo. In light to moderate traffic I try to keep my RPMs at 3000-3500. Cruising I'll slip into 5th gear at 70 but still around 2800-3200. Does that sound right?

In light traffic (30-50mph), if I get into 5th it lugs waaaay too much and does it in 4th too. I'm probably just getting used to a boxer engine. This was my first weekend on the bike after bringing her back to life...so I haven't checked the mileage (Bing 40s, removed the EGR and its dual plugged) and not sure what to expect if I ride sanely.

Any thoughts?

No its not right. Your speed is reading to high for the indicated rpm.

It sounds as if your speedometer is ready 10mph or so fast at 70mph. This is very common for this vintage airhead. What you should do is use a chart like the one suggested to you to tape a speed to expect on your tach in a certain gear at a certain rpm for reference. Usually the tachs and odometers are accurate.

 

[The_Veg]

Is it to late to reconsider my vote for the board position? I thought you were responsible and respectable. I guess that is the risk of only knowing people online.

This ain't the Goldwing club!

 

[AnnapolisAirhead]

No its not right. Your speed is reading to high for the indicated rpm.

It sounds as if your speedometer is ready 10mph or so fast at 70mph. This is very common for this vintage airhead. What you should do is use a chart like the one suggested to you to tape a speed to expect on your tach in a certain gear at a certain rpm for reference. Usually the tachs and odometers are accurate.

Ok, I think this is all due to my lack of experience on an airhead. I did try it out at higher revs and yes, vibration stopped. So commuting to and from work (37 miles each way) will be a lot of stop and go on the DC beltway...but when it does open up, it seems happiest at 70-75 in 5th. If I need to accelerate a shift down to fourth should do it.

I thought about a F650GS to commute, but I love the way this bike feels. Solid, tractor like and easy. Thanks for the help.

 

[Jeff488]

My bike is the same as yours, and I get about 66 mph at an indicated 4000 rpm.
4000 to 4300 seems to be a sweet spot for mine.
You could check your speedo and/or tach if you have a gps.
That's what I did when the speedo lost its mind. Sent it off to the psychiatrist(Overseas Speedometer in Austin, TX) and it came back sane and quite accurate(1 to 2 mph higher than actual).

 

[lkchris]

A large carb r100 (your 83) is much happier over 4k and even over 5k then under 4k. If you get on the throttle you will notice the vibration in your mirrors present at 4k will disappear at 5k if your carbs, valves and timing are correct. At 6k it will feel as smooth as a 4 cylinder. If you are feeling the engine pulses at 3k you are seriously lugging the engine which is bad for the engine and drive train. Try to be over 4k if you are putting any load on your engine, It won't hurt the milage and the drive train will thank you for it with a longer lifespan.

Everything stated above is simply incorrect.

There is NO SUCH THING as an engine that requires high revs to live and there is NO SUCH THING as an engine that gets better fuel mileage the higher it's revved.

But, it does make you feel manly.

Everything will last longer and you'll get better fuel economy the sooner you get it into 5th. Not in city traffic, obviously.

PS: Lugging in 5th gear on the subject R100 occurs around 2500 rpm. Higher if you really get on it. Just don't--this is not rocket science it's simply how to drive--anything.

 

[tkpinsc]

Everything stated above is simply incorrect.

There is NO SUCH THING as an engine that requires high revs to live and there is NO SUCH THING as an engine that gets better fuel mileage the higher it's revved.

But, it does make you feel manly.

Everything will last longer and you'll get better fuel economy the sooner you get it into 5th. Not in city traffic, obviously.

PS: Lugging in 5th gear on the subject R100 occurs around 2500 rpm. Higher if you really get on it. Just don't--this is not rocket science it's simply how to drive--anything.

Extreme lugging occurs when the bike is shuddering and you feel the engine pulses travel through the drivetrain. In this case he described the sensation at 3k on the highway. You can make most any engine lug at any rpm by applying a load approaching the power the engine is producing at that rpm. Reducing the gear is one way to apply less load to the engine. Producing more power by increasing rpms is another way to limit lugging.

The sweet spot for mileage is the same as the engines most effcient operating rpm - where the engine converts fuel and oxygen into energy with as little unburned fuel as possible. You may notice that it can take less throttle to maintain travel speed in a lower gear then a gear that is to high for the engine at that speed/load. This excess throttle is another sign of an engine that is being lugged. Detonation is also usually present when an engine is being lugged.

Each engine designs sweet spot is different depending on cam timing, ignition timing, intake tract and carburation, exhaust system, compression, stroke, displacement, combustion area design, valve size and placement and a host of other factors.

As far as everything living longer in 5th, the straight cut 1st - 4th gears will transfer loads better and with less wear on the gearbox then the helical cut 5th, although 5th is quieter.